Composition for addition to cast iron or steel



Patentecl May 29, 1951 COMPOSITION FOR ADDITION TO CAST IRON OR STEELJerome Strauss, New York, N. Y., assignor to Vanadium Corporation ofAmerica, New York, N. Y., a corporation of Delaware No Drawing.Application September 7, 1950, Serial No. 183,661

8 Claims.

This invention relates to a novel composition of matter for the controland improvement of the physical properties of cast iron and for otheruses, such as the treatment of steel in the molten state.

Cast iron is a generic term which includes gray irons, white cast irons,chilled cast irons and malleable irons. The properties of these metalsdepend in part upon chemical factors (principally the percentages ofcarbon and silicon) and in part upon physical factors, both asinfluenced by conditions related to the manufacturing methods. This isso because cast iron is essentially the product of a process and theinfiuence of the process details are observed in the qualities of theproduct. Alloying is employed to alter the properties of some castirons; also some iron castings both alloyed and not alloyed aresubiected to thermal treatments to produce desired results in castingfor specific uses. Th physical structure (i. e. the nature anddistribution of the micro constituents), and consequently the propertiesof the metal are influenced not only by these several factors but alsoby adjusting the maximum temperature attained by the molten iron and thecooling rate both during and after solidification.

Cast iron is sometimes considered unsatisfactory as a material ofconstruction because of its low strength and lack of ductility whencompared to steel and certain other engineering alloys. In such acomparison cast iron is usually described as being inherently brittle,especially in the ascast condition; this brittleness can be reduced onlyto a very limited extent by heat-treatment, except for long and costlytreatments applied to irons in the malleable iron composition range.

The cast iron which is most used commercially for constructionapplications, however, is gray iron, but this term actually covers aWide range of compositions with corresponding widely varying properties.The composition of gray iron is usually confined within the limits 0.50to 2.75% silicon and 2.70 to 3.60% total carbon. Within this range ofcomposition the tensile strength may vary from 15,000 to 60,000 poundsper square inch and occasionally higher.

While a part of the carbon present in gray cast iron may be in thecombined form as iron carbide, the greater amount is present inelemental form as graphite. The relative amounts of free carbon andcombined carbon, as well as the shape, size and distribution of theparticles are dependent upon the remaining chemical composition of theiron and the influences referred to above, namely,

maximum temperature in the liquid state, rate of cooling during andafter solidification, and types of heat treatment, if any, applied to asolidified casting.

Elements incidental to the production of cast iron may add or detractfrom its properties, such as strength, toughness and ductility. Sulphur,for example, is usually kept as low as possible because while itincreases the strength of the iron to some degree, it very markedlyreduces ductility. Control of sulphur depends, however, on raw materialsand process and often it cannot be held to very low values because onlyhigh-sulphur raw materials are available, the cost of electric furnacerefining may not be permissible and chemical treatment may not beadequate or sufficiently uniform. Phosphorus occasionally strengthensiron but in large amounts renders it quite brittle.

Certain elements usually considers as alloying agents have been added tocontrol the structure and properties of cast iron. In some cases theaddition of such alloys results in one property being improved to thedetriment of another, for example, strength may be improved but thetoughness of the iron be reduced unless some adequate form ofheat-treatment is provided to retain the toughness. In other casesimprovement in strength is accompanied by reduction in the machinabilityof the iron; in some of these cases heat-treatment, such as annealing,may restore the machinability.

It is known that magnesium added to iron which would otherwise cast grayor nearly so contributes to this iron high strength and some ductility.The ductility has in some cases been found to be increased by anannealing treatment with relatively little sacrifice in this superiorstrength.

However, serious difficulties have beset attempts to make this magnesiumpractice one that would provide with assurance successive reproductionin continuous manufacturing operations of iron articles of high strengthor high strength and good ductility. The boiling point of magnesiumbeing considerably below both the melting temperatures of those metalswith which it is preferably combined for making additional agents andbelow the temperatures at which cast iron is tapped and poured, causesextreme diniculty in controlling the overall recovery of magnesium fromraw material to the finished cast iron product.

The boiling point of magnesium is about 2030 E, which results in veryhighlosses due to Vaporization of the magnesium when it is added tomolten copper and molten nickel to produce such addition agents as 20%magnesium and 80% copper, and 20% magnesium and 80% nickel. Furtherdifficulty is presented when it is attempted to introduce iron intothese compositions. Iron is a very desirable carrier metal whenmagnesium is to be introduced into iron alloys, such as gray cast ironor steel. The introduction of iron into the copper or nickel base alloysmentioned above, however, only increase the already high losses ofmagnesium during manufacture.

Since the temperature of cast iron flowing from the cupola is normallyin the range 2300 to 2800 F., it is obvious that additional losses willbe encountered through vaporization when magnesium alloys are added toiron. When pure metallic magnesium is added to cast iron at such pouringtemperatures, its volatilization can be explosive in character.Magnesium continues to vaporize as long as the iron remains molten andthe time element combined with the initial violent reaction results invariable losses and properties that vary beyond the limits ofsatisfactory commercial control. The use of alloy addition agents, suchas the 20% magnesium and 80% copper, and 20% magnesium and 80% nickelcomposition previously mentioned, does not satisfactorily overcome thesedifilculties. For example, if the cast iron to which such alloys areadded is on the high side of the above temperature range, a violentreaction will occur with high losses of magnesium through volatilizationas well as loss of metal and danger to the operators through spatteringof the molten cast iron. If, on the other hand, the temperature of theiron is low, incomplete solution may occur, resulting in segregation andin variation in both structure and properties throughout the product.

I have discovered in the course of extended experiments directed towardthe development of a commercially satisfactory practice for producingmagnesium-containing cast iron of predictable and reproducibleproperties that certain combinations, preferably in alloy form, ofmagnesium, silicon, copper and iron afford an unexpected means ofsimplification of these problems. Primarily, my discovery consists in acertain critical combination in the proportions of magnesium, silicon,copper and iron, which substantially increases the recovery of magnesiumin manufacture of the addition agent as well as when this agent is addedto molten cast iron. This combination of effects results in asubstantial cost saving. More significant, however, is the fact that,when using alloys of compositions within the limits of my invention, thedesired improvements in the finished cast iron are obtainable morereadily and with much greater regularity. While cast iron in whichsubstantially all of the carbon is in the form of spheroids has beenproduced frequently, it has been difficult to obtain structurallyperfect casting under production conditions with a variety of designs,melting equipment, raw materials and other foundry conditions. Aninfinitely closer approach to perfection can be attained in the use ofthe alloy herein described. The mechanism of the behavior of thismagnesium-silicon-copper-iron compositions within the critical rangeshereinafter set forth has not been fully explained but the results havebeen obtained with such regularity both in production of the alloy and.in its use with gray cast iron over a substantial amount of productionand a large number 01. 1

'4 ferent foundries that a distinct advance in the art through its usehas been established.

The ranges of composition which have produced the advantages describedare 5 to 25% magnesium, 20 to 45% silicon, 3 to 20% copper, the balancesubstantially all but not less than 20% or more than 60% iron, exceptfor customary impurities and minor elements, such as carbon, manganese,sulphur, phosphorus, etc., which generally do not exceed a total of 5%.Nickel is not included among these minor elements; it is present todayin some pig irons and in most iron and steel scrap and hence may bepresent in these alloys up to about 2% and is not detrimental to thefunctioning of the alloys. In my compositions, aluminum is a detrimentalelement. It should be kept below 1% and preferably below 0.6%. Withinthe ranges of composition already cited, I prefer to restrict therelationship of the several elements so that the ratio of silicon tomagnesium is not less than about 2:1 and not greater than about 6: 1 andpreferably not greater than 4.5: 1, and the ratio of magnesium to copperis not less than 1:2 and not greater than 4:1 and preferably not greaterthan 2.5: 1. Following are three examples of compositions within thesecritical ranges and possessing the preferred ratio of elements whichwere manufactured and used successfully.

Iron Bal. Bal. Bill.

The definite advantages obtained with an iron content between 20% and60% are twofold: the iron increases the specific gravity of the alloy,aiding it to penetrate the molten metal, and it raises the meltingpoint, thus slowing down the rate of solution in the molten cast iron,effecting more uniform distribution throughout the mass. In addition tomelting too rapidly in the absence of iron, the cost of productionbecomes excessive if the iron is held below about 20%. If the ironcontent is permitted to exceed 60%, then the magnesium losses duringmanufacture of the alloy become excessive and very costly, and the rateof solution of such alloys in molten cast iron is too slow and theireffectiveness is greatly impaired.

By use of alloys having compositions within the described limits,superior results have been achieved in respect to formation of nodulesof graphite in cast iron and reduction of shrinkage of cast iron, overand above what had been previously attained by the best known and mostwidely used alloy, namely, nickel and 20% magnesium, together with thedevelopment of maximum amounts of tensile strength.

In addition, quite unexpectedly, it has been discovered that the slagforming on iron following the addition of magnesium-containing agents ismuch more fluid when using the alloys of this invention instead ofpreviously known magnesium alloys, thus avoiding slag entrapment in thefinished castings.

The amount of alloy added to molten cast iron to be cast into gray ironcastings varies with the nature of the iron (as influenced by the rawmaterials used and the conditions of processing during melting), themaximum temperature attained by the molten iron, the temperature at ofthe iron and perhaps other factors. In general, the additionapproximates 0.12% to 0.20% of contained magnesium plus an amount ofcontained magnesium equal to 1 times the sulphur content of the iron.This is not an absolute amount but varies according to the precisecomposition of the ailoy being used as well as the various factorsinfluencing the character of the molten cast iron, as pointed out above,and the method of adding the alloy to the molten iron. It is, however, agood starting point in establishing the practice in a specific foundrywhile on a particular melting practice so that a limited amount ofexperimentation varying the addition upward and downward readilyestablishes the optimum addition required. In general, the amount ofalloy added should be such as to have in the solidified cast iron atotal magnesium content of 0.04 to 0.10%, preferably 0.05 to 0.08%.

Another advantage possessed by these alloy addition agents is that ofincreased recovery of magnesium during both the manufacturing processand during use in the treatment of gray iron. Alloys Within these rangesof composition have the peculiar characteristic of being dissolvedsufliciently easily, in cast iron that they may be effectively used atthe lowest customary pouring temperatures which characterize moderncommercial foundry practice. On the other hand, solution. issufficiently slow that the alloy and its components will be uniformlydistributed throughout the melt and the magnesium will not be lost sorapidly as to prevent it from exerting its influence throughout theentire mass of cast iron. No additional care and no modifications ofprior practice are required, the addition of the alloy to iron thatwould otherwise cast gray, and of low moderate strength, being the solerequisite. The reason or reasons why these alloys melt at such criticalrates so as to be usable at full effectiveness over such a wide range ofcasting temperatures, but still melt slowly enough so that allingredients, and particularly the magnesium are distributed uniformlythroughout the cast iron have not been clarified but the observationshave been sufficiently numerous to be conclusive.

When alloys within composition ranges of the present invention are addedto cast iron, in-

creases in strength are secured ranging from about 50% to well over100%. In improving the mechanical properties to such high degrees thealloys covered by this invention regulate the microstructure of the grayiron so as to produce nodular graphite in the required amount, usuallyto the extent of complete conversion of the carbon to this form.

The following is an example of the procedure used in practicing thepresent invention.

EXAMPLE 1 Five hundred pounds of cast iron were poured into a ladlecontaining twenty pounds of alloy having the following composition:

Per cent Magnesium 5.67 Silicon 32.82 Copper 5.80 Iron Balance Thecomposition of the cast iron before and after treatment with the alloyis shown in Table 'I.

TABLE I Composition of treated and untreated iron 3 5 Manufacture 'r.o.Mn er s P Mg Cu 1 Untreated. 3.77 .69 1.65 .11 .19 None .11 2 Treated...3.10 .67 3.36 .01 .16 .075 .38

) Benefit to the iron by treatment with the alloy may be seen in TableII; where the hardness is shown to have been greatly increased andtensile strength has been more than tripled.

In a second example, samples were taken of the untreated iron, of theiron after treatment with an alloy containing 5.88% magnesium, 34.05%silicon and 5.56% copper, balance iron, and of the treated iron afterannealing. Compositions of these three samples are given in Table III.

TABLE III Sample Manufacture 'I. 0. Mn Si S P Mg Cu 3 Untreated 3.79 .782.43 .142 0.20 None .09 4 Treated.-." 3.20 .74 4.15 .011 0.19 .002 .35 5Treated and 3.18 .74 4. 22 .010 0.19 .094 .35

Annealed.

In this case the iron was of low strength, due possibly to its highsilicon and carbon contents,

but after treatment strength was more than doubled and the hardness wasgreatly increased as may be seen in Table IV.

TABLE IV Tensile Brinell Sample Manufacture Strength, Hardness p. s. i.No.

provement in machinability without reducing the strength.

EXAMPLE 3 iron and the cast iron treated with the same addition alloy aswas used in Example 2 are given in Table V.

TABLE V Sam- Manufacpi 6 mm '1 0. Mn S1 S 6 Untreated". 3.30 .65 1.61.12 .12 None .09 7 Treated 2.93 .60 3.18 .14

The compositions of another untreated cast In this case the treated anduntreated coupons were tested in the as-cast condition.

TABLE VI Tensile Brinell Sample Manufacture Strength, Hardness p. s. i.No.

6 Untreated 33, 600 190 7 Treated 95, 750 283 While the advantages of myinvention are obtainable with alloys within the composition rangealready given, namely, magnesium 5 to 25%, silicon 20 to 45%, copper 3to 20%, iron 20 to 60%, I prefer to use alloys with compositions Withinthe following narrower limits in order to develop the best propertieswith most economic advantages.

Per cent Magnesium '7 to 14 Silicon 25 to 38 Copper 5 to 12 Iron 35 to55 EXAMPLE 4 An alloy containing 13.52 magnesium,

33.80% silicon, 9.87% copper, balance iron, was used in the treatment ofelectric furnace iron. The analysis of the treated electric furnace castiron was:

Properties of the electric furnace cast iron as cast and after annealingwere as follows:

TABLE VII Yield Tensile Elong., R. A., Brinell Izod Point, Strength, PerPer Hard- Impact, p. s. i. p. s. i. Cent Cent ness Ft.-Lbs.

As-Oast. 67, 500 87, 200 1. 5 269 39 Annealed. 61, 500 85, 400 3. 0 2.229 183 These properties are far superior to those obtained fromordinary electric furnace cast iron.

EXAMPLE 5 The same alloy as given in Example 4 was used to treat cupolacast iron, which gave the following analysis after treatment:

Per cent Carbon 3.50 Silicon 2.60 Manganese .15 Phosphorus .025 Sulphur.015 Magnesium .050 Iron Balance The properties obtained in the as-castand annealed states were as follows:

TABLE VIII Yield Tensile Elongn, R. A., Brinell Izod Point, Strength,Per Per Hard- Impact, p. s. i. p. s. i. Cent Cent ness Ft.-Lbs.

As-Cast 52, 800 74, 700 ll. 0 8. 8 187 50 Annealed. 48, 900 66, 200 17.2 15.0 163 260 Methods of sampling and analysis currently in use showafter the addition of the alloys of this invention that the carboncontent and the sulphur content of the untreated irons have been reducedby the treatment. The reduction in the sulphur content is no doubt dueto the combination of magnesium with at least part of the sulphur andits removal as a slag or a slag forming constituent. The reason for thechange in the carbon content is not so obvious and it may be that thechange is apparent rather than real due to the difference in the formand the distribution of the carbon and creating a necessity fordifferent methods of sampling and analysis than those commonly in use.Completely satisfactory procedures have not yet been devised ordiscovered.

It has heretofore been an absolute requirement in the production of castiron having all or nearly all of its carbon in the form of spheroidsthat there be added following the addition of the magnesium alloy asecond addition rich in silicon, such as ferrosilicon, the amount inmost cases being substantial. In the use of the alloys of this inventionsuch final addition of ferrosilicon is not a necessity and may bedispensed with in many cases. The amount of silicon represented by theaddition of the alloys according to my invention is very much less thanthat which would be added according to prior art methods subsequent tothe incorporation of the magnesium alloy. Even in those instances wherea final addition of silicon-rich alloy is made, the total siliconcontent represented by this addition plus the silicon content added bymeans of the magnesium-silicon-copper-iron alloy is distinctly less thanthe silicon added as a late ferrosilicon addition according to prior artmethods. When the late ferrosilicon addition is actually employed inconjunction with the alloys of this invention, the maximum amount offerrite in the microstructure may be attained with a minimum siliconaddition, leaving not more than a very small amount of pearliticstructure in the matrix and through this means advantage in respect ofmachinability and reduction in the wear on tools used for machining willresult. Production of an iron with minimum pearlite also results inmaximum ductility of the iron composition.

The behavior in use of alloys with and without the prescribed amounts ofcopper have been compared in manufacture and use. Copper in theselimited amounts aids in the manufacture of the alloys, adds to thestability and melting characteristics, and very significantly improvesthe regularity of the production, as well as improving the properties ofthe cast iron after treatment. At the same time the copper content isnot so high that normal remelting of returns (heads, gates, etc.) withnew pig iron, other iron scrap, etc., causes an undesired building up ofthe copper content of the product which might adversely affect somecastings.

While fairly satisfactory results can be obtained in some instances inthe treatment of cast iron with compositions of matter within the rangespreviously specified, not in the form of alloys but in the form ofmechanical mixtures, much better results are obtained by the use ofthese compositions in alloy form.

Alloys of this invention have also been added to molten steel forlowering the sulphur content of the steel. For example, steels have hadtheir 9 sulphur content decreased from about .030 to about 020% by theuse of these alloys.

The invention is not limited to the preferred embodiment but may beotherwise embodied or practiced within the scope of the followingclaims.

I claim:

1. A composition of matter for addition to cast iron or steel, saidcomposition comprising about to 25% magnesium, to 45% silicon and about3 to 20% copper, the balance being substantially all iron, the ironbeing in an amount between about 20 and 60%.

2. A composition of matter for addition to cast iron or steel, saidcomposition comprising about 7 to 14% magnesium, about to 38% siliconand about 5 to 12% copper, the balance being substantially all iron, theiron being in an amount between about and 55%.

3. An alloy for addition to cast iron or steel, said alloy comprisingabout 5 to 25% magnesium, 20 to silicon and about 3 to 20% copper, thebalance being substantially all iron, the iron being in an amountbetween about 20 and 60%.

4. An alloy for addition to cast iron or steel, said alloy comprisingabout 7 to 14% magnesium, about 25 to 38% silicon and about 5 to 12%copper, the balance being substantially all iron, the iron being in anamount between about 35 and 5. An alloy for addition to cast iron orsteel, said alloy comprising about 5 to 25% magnesium,

about 20 to 45% silicon and about 3 to 20% copper, the ratio of siliconto magnesium being between about 2:1 and 6:1, the balance beingsubstantially all iron, the iron being in an amount between about 20 and6. An alloy for addition to cast iron or steel, said alloy comprisingabout 5 to 25% magnesium, about 20 to 45% silicon, and about 3 to 20%copper, the ratio of magnesium to copper being between about 1:2 and4:1, the balance being substantially all iron, the iron being in anamount between about 20 and 60%.

7. An alloy for addition to cast iron or steel, said alloy comprisingabout 5 to 25% magnesium, 20 to 45% silicon and 3 to 20% copper, theratio of silicon to magnesium being between about 2:1 and 6:1, the ratioof magnesium to copper being between about 1:2 and 4:1, the balancebeing substantially all iron, the iron being in an amount between about20 and 60%.

8. An alloy for addition to cast iron or steel, said allo comprisingabout '7 to 14% magnesium, about 25 to 38% silicon, and about 5 to 12%copper, the ratio of silicon to magnesium being between about 2:1 and45:1, the ratio of magnesium to copper being between about 1:2 and2.5:1, the balance being substantially all iron, the iron being in anamount between about 20 and 60%.

JEROME STRAUSS.

No references cited.

1. A COMPOSITION OF MATTER FOR ADDITION TO CAST IRON OR STEEL, SAIDCOMPOSITION COMPRISING ABOUT 5 TO 25% MAGNESIUM, 20 TO 45% SILICON ANDABOUT 3 TO 20% COPPER, THE BALANCE BEING SUBSTANTIALLY ALL IRON, THEIRON BEING IN AN AMOUNT BETWEEN ABOUT 20 AND 60%.